Personal computers have become very common in business and commercial organizations. Such computers usually include a processing unit, disk storage, display and a single keyboard. Other peripherals may be connected to the processing unit.
The processing unit usually includes a microprocessor. Several different types of microprocessors have been used. An INTEL type 80286 microprocessor has been used in the implementation of International Business Machines Model AT personal computer, as well as, AT-type imitations thereof. The 80286 processor has a 16 bit bidirectional data bus and a 24 bit unidirectional address bus. AT-type computers are discussed in Using and Programming the IBM PC AT, by T. Petersen; Prentice-Hall, 1987, incorporated herein by reference.
AT-type computers are usually used with an operating system such as PC-DOS or MS-DOS. AT-type computers have a multi-conductor single keyboard input. There are circumstances where it would be desirable to associate a plurality of keyboards with a given AT-type computer. In such an instance, it would be desirable to be able to select one keyboard from the plurality as the active one.
AT-type computers monitor one of the keyboard input lines. A loss of signal for an extended period of time requires that the operating system be rebooted or reinitialized. Such an operation can result in a loss of recently entered information and/or damage to records which are open at that time.
In addition, it would be desirable to be able to associate a display with each keyboard. Preferably, coupling the selected keyboard to the computer and driving the displays can be carried out in a cost effective fashion.